Temperature-dependent fecundity and survival data was integrated into a matrix population model to describe relative Drosophila suzukii Matsumura (Diptera: Drosophilidae) population increase and age ...structure based on environmental conditions. This novel modification of the classic Leslie matrix population model is presented as a way to examine how insect populations interact with the environment, and has application as a predictor of population density. For D. suzukii, we examined model implications for pest pressure on crops. As case studies, we examined model predictions in three small fruit production regions in the United States (US) and one in Italy. These production regions have distinctly different climates. In general, patterns of adult D. suzukii trap activity broadly mimicked seasonal population levels predicted by the model using only temperature data. Age structure of estimated populations suggest that trap and fruit infestation data are of limited value and are insufficient for model validation. Thus, we suggest alternative experiments for validation. The model is advantageous in that it provides stage-specific population estimation, which can potentially guide management strategies and provide unique opportunities to simulate stage-specific management effects such as insecticide applications or the effect of biological control on a specific life-stage. The two factors that drive initiation of the model are suitable temperatures (biofix) and availability of a suitable host medium (fruit). Although there are many factors affecting population dynamics of D. suzukii in the field, temperature-dependent survival and reproduction are believed to be the main drivers for D. suzukii populations.
Abstract
Drosophila suzukii, or spotted-wing drosophila, is now an established pest in many parts of the world, causing significant damage to numerous fruit crop industries. Native to East Asia, D. ...suzukii infestations started in the United States a decade ago, occupying a wide range of climates. To better understand invasion ecology of this pest, knowledge of past migration events, population structure, and genetic diversity is needed. In this study, we sequenced whole genomes of 237 individual flies collected across the continental United States, as well as several sites in Europe, Brazil, and Asia, to identify and analyze hundreds of thousands of genetic markers. We observed strong population structure between Western and Eastern US populations, but no evidence of any population structure between different latitudes within the continental United States, suggesting that there are no broad-scale adaptations occurring in response to differences in winter climates. We detect admixture from Hawaii to the Western United States and from the Eastern United States to Europe, in agreement with previously identified introduction routes inferred from microsatellite analysis. We also detect potential signals of admixture from the Western United States back to Asia, which could have important implications for shipping and quarantine policies for exported agriculture. We anticipate this large genomic dataset will spur future research into the genomic adaptations underlying D. suzukii pest activity and development of novel control methods for this agricultural pest.
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•Populations of two parasitoids of Drosophila suzukii were tested under laboratory conditions.•Only the Italian population of Leptopilina heterotoma parasitized D. suzukii.•Italian ...and North American populations of Pachycrepoideus vindemiae parasitized D. suzukii.•Host pupal preference and lifetime fecundity of P. vindemiae were determined.•A third parasitoid species, Trichopria drosophilae, showed the ability to parasitize D. suzukii.
Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) causes severe damage to certain fruit crops in both North America and Europe. This may be due, in part, to the absence of specialized natural enemies that suppress population outbreaks. We performed a series of experiments under controlled laboratory conditions in tandem with a field study to evaluate the presence and efficacy of natural enemies associated with this pest in Italian and western United States fruit production regions. Our study involved one larval parasitoid, Leptopilina heterotoma (Thomson) (Hymenoptera: Figitidae), and two pupal parasitoids, Pachycrepoideus vindemiae (Rondani) (Hymenoptera: Pteromalidae) and Trichopria drosophilae (Perkins) (Hymenoptera: Diapriidae). Three indices were used to describe host-parasitoid interactions: degree of infestation (DI), success rate of parasitism (SP) and total encapsulation rate (TER). Results confirmed that each of these parasitoid species can develop on certain populations of the pest. In addition, host stage preferences of the tested parasitoid populations, developmental parameters and lifetime fecundity of North American P. vindemiae are provided. Results are discussed with respect to differences in potential utilization of D. suzukii among the tested parasitoid species and regional populations.
The invasive spotted wing drosophila,
Drosophila suzukii
Matsumura (Dipt.: Drosophilidae), a native of East Asia, has widely established in North America and Europe, where it is a serious pest of ...small and stone fruit crops. The lack of effective indigenous parasitoids of
D. suzukii
in the recently colonized regions prompted the first foreign exploration for co-evolved parasitoids in South Korea during 2013 and 2014. We collected the larval parasitoids
Asobara japonica
Belokobylskij,
A
.
leveri
(Nixon) and
A.
brevicauda
Guerrieri & van Achterberg (Hym.: Braconidae)
, Ganaspis
brasiliensis
(Ihering),
Leptopilina japonica japonica
Novković & Kimura and
L. j. formosana
Novković & Kimura (Hym.: Figitidae); and the pupal parasitoids
Pachycrepoideus vindemiae
(Rondani) (Hym.: Pteromalidae) and
Trichopria drosophilae
Perkins (Hym.: Diapriidae). From UC Berkeley quarantine records, percentage parasitism ranged from 0 to 17.1 % and varied by geography, season, and collection methods.
Asobara japonica
was the most common parasitoid species. Higher numbers of parasitoids were reared from field-picked fruit as opposed to traps baited with uninfested fruit. Quarantine bioassays confirmed that
A. japonica
,
G. brasiliensis
,
L. j
.
japonica
,
P. vindemiae
, and
T. drosophilae
developed from
D. suzukii
. Female individuals of the endoparasitoid,
A. japonica,
were larger when reared on the larger
D. suzukii
larvae compared with those reared on the smaller larvae of
D. melanogaster
Meigen. Larger parasitoid size was associated with longer developmental time. Several of the South Korean parasitoid species have the potential for use in classical biological control and may contribute to the suppression of
D. suzukii
in the newly invaded regions.
Pest spillover from wildlands to farms can create conflict between habitat conservation and agricultural production. For example, the key economic pest of hazelnuts in Oregon’s Willamette Valley is ...the filbertworm (
Cydia latiferreana
), a moth hosted by the native Oregon white oak (
Quercus garryana
). Oak habitat near hazelnut orchards can sustain source populations that compound pest load in hazelnuts throughout the growing season. This dynamic is of conservational concern as historical oak habitat has been greatly reduced and what remains is almost entirely on private land, often in proximity to hazelnut orchards. Here, we present a novel strategy to reconcile this regional conflict by using hogs (
Sus domesticus
) to reduce pest populations through prescribed foraging. From 2018 to 2020 we prescribed hog-foraging in early fall to glean filbertworm-infested acorns from an oak woodland understory. Hogs were both highly successful at reducing the total number of infested acorns and the ratio of infested acorns the following year. Despite an oak-masting year in 2019, foraging reduced both the emerging and adult mating population of filbertworm the following year. We did not measure significant changes in the woodland understory, suggesting intermittent hog-foraging may not entail tradeoffs for understory vegetation. Our results demonstrate that prescribed foraging in oak patches can be an effective strategy to reduce filbertworm source populations. By benefiting both conservation and farmers, this adaptive pest management approach provides a model for similar challenges and conflicts across the agricultural-wildland matrix.
Drosophila suzukii
causes economic damage to berry and stone fruit worldwide. Laboratory-generated datasets were standardized and combined on the basis of degree days (DD), using Gompertz and Cauchy ...curves for survival and reproduction. Eggs transitioned to larvae at 20.3 DD; larvae to pupae at 118.1 DD; and pupae to adults at 200 DD. All adults are expected to have died at 610 DD. Oviposition initiates at 210 DD and gradually increases to a maximum of 15 eggs per DD at 410 DD and subsequently decreases to zero at 610 DD. These data were used as the basis for a DD cohort-level population model. Laboratory survival under extreme temperatures when DD did not accumulate was described by a Gompertz curve based on calendar days. We determined that the initiation of the reproductive period of late dormant field-collected female
D. suzukii
ranged from 50 to 800 DD from January 1. This suggests that
D. suzukii
females can reproduce early in the season and are probably limited by availability of early host plants. Finally, we used the DD population model to examine hypothetical stage-specific mortality effects of IPM practices from insecticides and parasitoids at the field level. We found that adulticides applied during the early season will result in the largest comparative population decrease. It is clear from model outputs that parasitism levels comparable to those found in field studies may have a limited effect on population growth. Novel parasitoid guilds could therefore be improved and would be valuable for IPM of
D. suzukii
.
Insect parasitoids are often manipulated to improve biological control programs for various arthropod pests. Volatile compounds can be a relevant cue used by most parasitoid hymenoptera for host or ...host microhabitat location. Here, we studied olfactory responses of the braconid
Asobara japonica
Belokobylskij, an Asiatic endoparasitoid of the invasive pest
Drosophila suzukii
(Matsumura), toward its host and host substrates. Adult
A. japonica
displayed an innate attraction to undescribed volatile cues from infested host fruits irrespectively of the juvenile rearing experience, i.e. they respond to a novel cue subsequently used for microhabitat selection. These data suggest that
A. japonica
parasitoids mass-reared on artificial diet and factitious host (
D. melanogaster
) can successfully locate their hosts. Naïve female parasitoids did not show a preference towards any of the tested host media. However, the enforced adult experience with the rearing host medium modified the olfactory preference patterns toward non-natal host fruits. These findings provide evidence of associative learning during the adult stage of
A. japonica
, and demonstrate its plasticity in exploiting the volatiles from various fruits infested by
D. suzukii
.
Temperature-dependent fecundity and survival data was integrated into a matrix population model to describe relative Drosophila suzukii Matsumura (Diptera: Drosophilidae) population increase and age ...structure based on environmental conditions. This novel modification of the classic Leslie matrix population model is presented as a way to examine how insect populations interact with the environment, and has application as a predictor of population density. For D. suzukii, we examined model implications for pest pressure on crops. As case studies, we examined model predictions in three small fruit production regions in the United States (US) and one in Italy. These production regions have distinctly different climates. In general, patterns of adult D. suzukii trap activity broadly mimicked seasonal population levels predicted by the model using only temperature data. Age structure of estimated populations suggest that trap and fruit infestation data are of limited value and are insufficient for model validation. Thus, we suggest alternative experiments for validation. The model is advantageous in that it provides stage-specific population estimation, which can potentially guide management strategies and provide unique opportunities to simulate stage-specific management effects such as insecticide applications or the effect of biological control on a specific life-stage. The two factors that drive initiation of the model are suitable temperatures (biofix) and availability of a suitable host medium (fruit). Although there are many factors affecting population dynamics of D. suzukii in the field, temperature-dependent survival and reproduction are believed to be the main drivers for D. suzukii populations.
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